Sensor elements which operate on the basis of magnetic influence on elements which change their resistance upon change of a magnetic field to which they are exposed are known--see, for example, the referenced textbook, Siemens Data Book, Vol. 1, chapter on "Sensors", particularly pages 60-69. Sensors of this type have two magnetic field resistors which are serially connected to a source of direct current. The sensor voltage is tapped off at the junction of the two resistors.